This invention relates to a system for controlling the energization of electromagnets disposed adjacent vertical guide rails in an elevator installation.
In older elevator systems the cage is typically guided during its upward and downward travel by shoes or rollers mounted to the cage and engaging vertical rails fixed to the walls of the elevator shaft or hoistway. If the joints between any two successive rail elements are misaligned or migrate out of alignment with use, however, the cage is subject to shaking and vibration as the shoes or rollers traverse the joints. Such jostling obviously leads to fear and apprehension in the passengers.
To overcome this problem a contactless guide system has been developed as disclosed in Japanese Kokai No. 51-116548 and as illustrated in FIGS. 1 through 4, wherein T-shaped iron guide rails 1 are mounted to the opposite walls of an elevator shaft 2 housing a passenger cage 5 having a frame 3 suspended by ropes or cables 4. Three electromagnets 6, 7 and 8 are secured to the top and bottom of the frame on opposite sides of the cage, and surround the guide rails 1 as best seen in FIG. 2. The magnets have C-shaped iron cores 9, 10, 11 respectively wound by coils 12, 13, 14, and their end faces are spaced or gapped from the adjacent surfaces of the guide rails. Although not fully illustrated, there are four groups of three magnets each as will be readily understood. A detector 15 is mounted next to the core 10 for sensing the gap between the end faces of the core and the side of the rail 1. A detector 16 mounted next to core 11 similarly senses the gap at the innermost portion of the rail, and a further gap detector 17 is associated with magnet 7A on the opposite side of the cage frame.
The control circuit for coils 12 and 13 is shown in FIG. 4, wherein differential firing circuits 21, 22 control the firing angles of thyristors 19, 20 coupled between the respective coils and AC power source 18 in response to the output of gap detector 15. Similar control circuitry would be provided for magnets 6A, 7A associated with detector 17, magnets 8, 8A associated with detector 16, as well as the three magnet pairs and associated gap detectors mounted to the bottom or underside of the cage frame.
In operation, and referring first to opposing magnets 6 and 7, when the gap sensed by detector 15 is equal to a predetermined value thyristors 19 and 20 are fired at the same angle and thus apply equal energization to the coils 12, 13 whereby the magnets 6, 7 equally attract (or repel) the centered guide rail 1. If the gap between core 10 and the side of the rail decreases, however, the increased output of detector 15 differentially controls the firing circuits 21, 22 such that the energization of coil 12 is increased while that of coil 13 is decreased. The resulting differential or unequal forces generated by the opposing pair of magnets 6, 7 thus acts to re-center the guide rail between them, as may be easily understood. The other five pairs of cooperating or associated electromagnets are differentially controlled in a similar manner in response to the outputs of their respective gap detectors such that the guide rails are maintained centered as shown in FIG. 2 to define equal opposing air gaps and smoothly guide the cage during its travel without any disruptive physical contact with the rails.
The performance of such a conventional contactless guide system is still fully dependent on the precise axial alignment of the successive vertical guide rails, however, which as a practical matter is almost impossible to accurately establish and maintain. Thus, if a joint between two successive rails migrates laterally due to settling, thermal expansion or the like as exaggeratedly shown in FIG. 3, the cage is subjected to shaking and vibration as the centering magnets strive to follow the misaligned joint. The problem can be corrected by realigning the guide rails, but this is obviously very labor intensive, disruptive and costly.